A Potential New and Easy Way to Make Attosecond Laser Pulses: Focus a Laser on Ordinary Glass

This novel method could shrink the equipment needed to make laser pulses that are billionths of a billionth of a second long for studying ultra-speedy electron movements in solids, chemical reactions and future electronics.

Credit: Greg Stewart/SLAC National Accelerator Laboratory

In this illustration, a near-infrared laser beam hits a piece of ordinary glass and triggers a process called high harmonic generation. It produces laser light pulses (top right) that are just billionths of a billionth of a second, or attoseconds, long, and the photons in those pulses are much higher energy than those in the original beam. The insets zoom in on how this happens. When the incoming laser light knocks electrons (e-) out of atoms in the glass, they fly away, loop back and reconnect with either their home atom (lower right) or a neighboring atom (upper left). These reconnections generate bright bursts of light, forming a “train” of attosecond pulses that leaves the glass and can be used to probe electron movements in solids.

The discovery 30 years ago that laser light can be boosted to much higher energies and shorter pulses - just billionths of a billionth of a second, or attoseconds, long - is the basis of attosecond science, where researchers observe and try to control the movements of electrons. Electrons are key players in chemical reactions, biological processes, electronics, solar cells and other technologies, and only pulses this short can make snapshots of their incredibly swift moves.

Now scientists from the Stanford PULSE Institute at the Department of Energy’s SLAC National Accelerator Laboratory have found a potential new way to make attosecond laser pulses using ordinary glass - in this case, the cover slip from a microscope slide.

The discovery, reported in Nature Communications today, was a real surprise and opens new possibilities for attosecond science and technology, including the ability to probe ultra-speedy electron motions inside glasses and other solid materials. It could also dramatically shrink the size and cost of the setups needed to produce these tiny pulses, to the point where you might be able to generate pulses inside a fiber optic cable that delivers them to where they’re needed.

“With today’s methods, you have to shine the laser beam through a special gas jet or through a crystal that has to be grown with great care at ultra-cold temperatures,” said Yong Sing You, a postdoctoral researcher at PULSE and lead author of the study. “But this is exciting because you can use everyday glass, which is cheap and easily available, at room temperature. If you were to put your eyeglasses into the experiment, it would still work, and it would not even damage the glasses.”

A String of Surprises

The process that generates attosecond laser pulses is called high harmonic generation, or HHG. Much like pressing on a guitar string produces a note that’s higher in pitch, shining laser light through certain materials changes the nature of the light, shifting it to higher energies and shorter pulses than a laser can reach on its own.

Most of the time this is done in a gas. Incoming photons, or particles of light, from the laser hit atoms in the gas and liberate some of their electrons. The freed electrons fly away, loop back and reconnect with their home atoms. This reconnection generates attosecond bursts of light that combine to form an attosecond laser pulse.

Starting in 2010, a series of experiments led by PULSE researchers Shambhu Ghimire and David Reis showed HHG can be produced in ways that were previously thought unlikely or even impossible: by beaming laser light into a crystal, frozen argon gas or an atomically thin semiconductor material.

Unlike a gas, whose atoms are so far apart that you can think of them as behaving independently, atoms in a solid are so close together that scientists thought electrons freed by an incoming laser pulse would hit neighboring atoms, scatter and never return home to make that crucial reconnection. But it turned out this was not the case, Reis said: “There’s something about the orderly structure of the crystal that allows electrons to move throughout the lattice in a way that doesn’t dissipate their energy or give them a kick in some other direction. Even if they connect with a neighboring atom, they can still participate in HHG.”

Fundamental Science with Practical Potential

The fact that glass could generate HHG was also a surprise, said Ghimire, who helped lead the latest study. Because it’s amorphous, meaning that its silicon and oxygen atoms are arranged in no particular order, it did not seem like a good candidate.

But glass’s random nature was just what the team needed to answer the fundamental scientific question at the heart of the study: How do the density and crystallinity of a material - the degree to which its atoms are arranged in an orderly lattice – independently affect its ability to produce HHG? A piece of glass and a quartz crystal are both made of silicon and oxygen, and they’re roughly the same density; only the arrangement of their atoms is different. So comparing the two should provide some answers.

The scientists put the glass cover slip in their apparatus and hit it with pulses from their infrared laser beam.

“You might think, again, that this wouldn’t work, because the electrons would bounce off their neighbors and never make it back home,” said Reis, who was not involved in the current paper. “But the surprising thing is that even in glass, if you hit the glass hard enough but not so hard that you break it, it works fine, although by a slightly different process.”

The ability to produce HHG in glass and other solids is exciting, he said, because it has the potential to shrink the equipment needed to do this from the size of a lab bench to maybe just a few nanometers - billionths of a meter - in size.

Ghimire added that producing harmonics in glass has potential technological applications. For instance, it produces the short wavelengths of laser light needed to design masks for patterning nanometer-scale features on semiconductor chips.

“For this, they want as much intensity as possible, and also an easy way to deliver light to their samples,” he said. “Being able to produce short-wavelength laser light in normal glass would bring us a couple of steps closer to something they could actually use. We could even generate the short-wavelength light in the glass portion of optical fibers that then deliver it to wherever they wanted it.”

The Stanford PULSE Institute is an independent laboratory of Stanford University as well as a research center within the SLAC Science Directorate. This research was done in collaboration with scientists at the University of Central Florida. The DOE Office of Science funded the work at PULSE through an Early Career Research Program award to Ghimire. The work in Florida was funded by the Air Force Office of Scientific Research, the Army Research Office, the DARPA PULSE program and the National Science Foundation.

SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, Calif., SLAC is operated by Stanford University for the U.S. Department of Energy's Office of Science. For more information, please visit slac.stanford.edu.

SLAC National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Filters

A team of researchers led by the Department of Energy's Oak Ridge National Laboratory has demonstrated a new method for splitting light beams into their frequency modes, work that could spur advancements in quantum information processing and distributed quantum computing.

Black women with higher incomes are more likely to experience a forceful police interaction during a traffic stop, finds a new study from the Brown School at Washington University in St. Louis."We found that the likelihood of exposure to each type of police use of force was significantly greater for black females with incomes over $50,000," said Robert Motley Jr.

Using high-intensity pulses of infrared light, scientists found evidence of superconductivity associated with charge "stripes" in a material above the temperature at which it begins to transmit electricity without resistance--a finding that could help them design better high-temperature superconductors.

In a recent demonstration project, physicists from Brookhaven National Laboratory and Berkeley Lab used the Cori supercomputer at the National Energy Research Scientific Computing Center to reconstruct data collected from a nuclear physics experiment, an advance that could dramatically reduce the time it takes to make detailed data available for scientific discoveries.

In light of changes in how electricity is being both generated and consumed, the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has written a new report analyzing challenges facing the nation's electric grid and making recommendations for ensuring continued reliability.

Scientists at the U.S. Department of Energy's Ames Laboratory have discovered a state of magnetism that may be the missing link to understanding the relationship between magnetism and unconventional superconductivity.

Filters

News Release PORTLAND, Ore. -- Pacific Northwest National Laboratory and OHSU today announced a joint collaboration to improve patient care by focusing research on highly complex sets of biomedical data, and the tools to interpret them.The OHSU-PNNL Precision Medicine Innovation Co-Laboratory, called PMedIC, will provide a comprehensive ecosystem for scientists to utilize integrated 'omics, data science and imaging technologies in their research in order to advance precision medicine -- an approach to disease treatment that takes into account individual variability in genes, environment and lifestyle for each person.

Forty-five years ago this month, a telescope tucked inside a 14-story, 500-ton dome atop a mile-high peak in Arizona took in the night sky for the first time and recorded its observations on glass photographic plates. Today, the dome closes on the previous science chapters of the 4-meter Nicholas U. Mayall Telescope and starts preparing for its new role in creating the largest 3-D map of the universe. This map could help determine why the universe is expanding at faster and faster rates, driven by an unknown force called dark energy.

Twenty-four teams from 16 Bay Area high schools faced off Feb. 3 in the SLAC Regional DOE Science Bowl, a series of fast-paced question-and-answer matches that test knowledge in biology, chemistry, physics, earth and space sciences, energy and math. The competition is hosted annually by the Department of Energy's SLAC National Accelerator Laboratory.

The University of Illinois at Chicago's Energy Resources Center has received funding from ComEd to provide energy-efficient LED light bulbs, advanced power strips, and educational material to income-qualified participants in northern Illinois.As part of a $3.1 million year-long investment, the utility company will fund the Low Income Kit Energy (LIKE) program, allowing engineers at UIC's Energy Resources Center to provide energy-saving kits to 35,000 eligible individuals and/or families.

The Department of Energy (DOE) on Feb. 1 announced up to $3 million will be made available to U.S. manufacturers for public/private projects aimed at applying high performance computing to industry challenges for the advancement of energy innovation.

UPTON, NY -- Elke-Caroline Aschenauer, a senior physicist at the U.S. Department of Energy's Brookhaven National Laboratory, has been awarded a Humboldt Research Award for her contributions to the field of experimental nuclear physics. This prestigious international award--issued by the Alexander von Humboldt Foundation in Bonn, Germany--comes with a prize of EUR60,000 (more than $70,000 U.

A team of networking experts from the Department of Energy's Energy Sciences Network (ESnet), with the Globus team from the University of Chicago and Argonne National Laboratory, have designed a new approach that makes data sharing faster, more reliable and more secure.